document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1157547>Question 1157547</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The current of a river is 2 miles per hour. It takes a motorboat a total of 3 hours to travel 8 miles upstream and return 8 miles downstream. What is the speed of the boat in still water? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #780419 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=780419\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> speed of motorboat in still water=s<BR>\n" );
document.write( "s-2 is speed upstream and if t hours, the distance is t(s-2)=8, and t=8/(s-2)<BR>\n" );
document.write( "s+2 is speed downstream and it is 3-t hours, and the distance is (s+2)(3-t)=8, so 3-t=8/(s+2), t=3-(8/(s+2)<BR>\n" );
document.write( "t=(3s+6-8)/(s+2)<BR>\n" );
document.write( "so (3s+6-8)/(s+2)=8/(s-2)<BR>\n" );
document.write( "cross-multiply<BR>\n" );
document.write( "3s^2-6s-2s+4=8s+16<BR>\n" );
document.write( "3s^2-16s-12=0<BR>\n" );
document.write( "(3s+2)(s-6)=0<BR>\n" );
document.write( "s=6 mph speed of boat in still water.\r<BR>\n" );
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document.write( "upstream at 4 mph takes 2 hours<BR>\n" );
document.write( "downstream at 8 mph takes 1 hour\r<BR>\n" );
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document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );